Fuel cell

ABSTRACT

Flow guides forming an inlet channel are formed on a surface of a metal separator of a fuel cell. The flow guides overlap a section of an outer seal provided on the other surface of the metal separator. When a load is applied to the flow guides and the overlapping section in a stacking direction of the fuel cell, the flow guides and the overlapping section are deformed substantially equally in the stacking direction to the same extent. The line pressure of the flow guides and the line pressure of the overlapping section are substantially the same. The seal length L 1  of the flow guides and the seal length L 2  of the overlapping section are substantially the same.

RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 12/537,488 filed Aug. 7, 2009 which is a continuation application ofU.S. application Ser. No. 10/835,670 filed Apr. 30, 2004, now U.S. Pat.No. 7,704,625 B2, which claims priority to Japanese Patent ApplicationNo. 2003-126551 filed May 1, 2003 and Japanese Patent Application No.2003-126561 filed May 1, 2003. The contents of the aforementionedapplications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fuel cell formed by stacking aplurality of power generation cells. Each of the power generation cellsincludes an electrolyte electrode assembly and separators sandwichingthe electrolyte electrode assembly. The electrolyte electrode assemblyincludes a pair of electrodes, and an electrolyte interposed between theelectrodes. The fuel cell has an internal manifold including reactantpassages and a coolant passage. The reactant passages and the coolantpassage extend through the power generation cells in the stackingdirection, and are connected to reactant flow fields and a coolant flowfield, respectively.

2. Description of the Related Art

For example, a solid polymer fuel cell employs a membrane electrodeassembly (MEA) which includes two electrodes (anode and cathode), and anelectrolyte membrane interposed between the electrodes. The electrolytemembrane is a polymer ion exchange membrane. The membrane electrodeassembly and separators sandwiching the membrane electrode assembly makeup a unit of a power generation cell for generating electricity. Apredetermined number of the power generation cells are stacked togetherto form a stack of the fuel cell.

In the power generation cell, a fuel gas such as a gas chieflycontaining hydrogen (hydrogen-containing gas) is supplied to the anode.The catalyst of the anode induces a chemical reaction of the fuel gas tosplit the hydrogen molecule into hydrogen ions (protons) and electrons.The hydrogen ions move toward the cathode through the electrolyte, andthe electrons flow through an external circuit to the cathode, creatinga DC electric current. A gas chiefly containing oxygen(oxygen-containing gas) or air is supplied to the cathode. At thecathode, the hydrogen ions from the anode combine with the electrons andoxygen to produce water.

Various sealing structures are used for preventing the leakage of thefuel gas and the oxygen-containing gas in the power generation cell. Forexample, a sealing structure disclosed in Japanese laid-open patentpublication No. 8-148169 uses a conventional O-ring. FIG. 11 shows thesealing structure of Japanese laid-open patent publication No. 8-148169.A membrane electrode assembly 3 includes an anode 2 a, a cathode 2 b,and an electrolyte membrane 1 interposed between the anode 2 a and thecathode 2 b. The membrane electrode assembly 3 is sandwiched between theseparators 4 a, 4 b. O-rings 5 a, 5 b are provided between theseparators 4 a, 4 b around the electrolyte membrane 1.

Typically, in the power generation cell, an oxygen-containing gas flowfield (reactant gas flow field) is provided on a surface of theseparator facing the cathode for supplying the oxygen-containing gas(reactant gas) to the cathode, and a fuel gas flow field (reactant gasflow field) is provided on a surface of the separator facing the anodefor supplying the fuel gas (reactant gas) to the anode. Further, acoolant flow field is provided between the separators for cooling thepower generation cells.

The fuel cell has an internal manifold structure in which a fuel gassupply passage and a fuel gas discharge passage (reactant gas passages)connected to the fuel gas flow field, an oxygen-containing gas supplypassage and an oxygen-containing gas discharge passage (reactant gaspassages) connected to the oxygen-containing gas flow field, and acoolant supply passage and a coolant discharge passage connected to thecoolant flow field extend through outer regions of the separators in thestacking direction. The reactant gas flow field may be connected to thereactant gas flow passages by connection channels formed by sealmembers. For example, in FIG. 12, a reactant gas flow field 7 a isformed on a surface 6 a of a separator 6 along a power generationsurface, and a reactant gas passage 7 b extends through the separator 6in the stacking direction.

A seal member 8 is provided on the surface 6 a of the separator 6. Theseal member 8 includes connection sections 8 a separately provided at anarea connecting the reactant gas flow field 7 a and the reactant gaspassage 7 b. The reactant gas flows through connection grooves 7 cbetween the separate connection sections 8 a. A seal member 9 isprovided on the other surface 6 b of the separator 6 for sealing thecoolant flow field (not shown).

The seal members 8 and 9 prevent the leakage of the reactant gas and thecoolant. Further, the load balance in the surface of the powergeneration cell should be uniform, and the load balance should notchange depending on the power generation cell in order to achieve theuniform, and the stabilized power generation performance in each of thepower generation cells. In particular, the pressure applied to the powergeneration cell should be kept at the desired level to stabilize thepower generation performance. Further, each of the power generationcells should have a uniform space in the flow field so that the crosssectional area of the flow field does not change depending on the powergeneration cell, and the uniform flow rates of the reactant gasdistributed from the reactant gas passage 7 b and the coolantdistributed from the coolant passage 7 d can be achieved.

According to the structure shown in FIG. 12, the connection grooves 7 cbetween the reactant gas flow field 7 a and the reactant gas passage 7 bare formed by the separate connection sections 8 a of the seal member 8.On the other surface opposite to the surface 6 a, a section 9 a of theseal member 9 extend along the sections 8 a continuously. Therefore,when a load in a stacking direction is applied to the connectingsections 8 a on the surface 6 a and the section 9 a which is provided onopposite surface, the connection sections 8 a and the section 9 a arenot deformed uniformly. Thus, the height difference between theconnection sections 8 a of the seal member 8 and the section 9 a of theseal member 9 occurs. Therefore, the cross sectional areas of thereactant gas channels in the seal members 8, 9 are not uniform.Consequently, the seal performance may not be good, and the reactant gascan not be supplied smoothly to the flow field due to the undesirableclosure of the gas channels.

When thin metal separators are used, the balance of the line pressure(load) is not uniform, and the separators tend to be deformed in thestacking direction. Thus, the pressure is applied to the sealing surfaceor the power generation surface excessively or insufficiently. As aresult, it is difficult to achieve the desired power generationperformance with the simple structure.

FIG. 13 shows a solid polymer fuel cell stack disclosed in Japaneselaid-open patent publication No. 2001-266911. For example, anoxygen-containing gas flow field S2 for supplying a reactant gas such asan oxygen-containing gas is formed in a serpentine pattern on a surfaceof a separator S1. The oxygen-containing gas flow field S2 is connectedto an oxygen-containing gas supply passage S3 and an oxygen-containinggas discharge passage S4 which extend through outer regions of theseparator S1 in the stacking direction. A packing S5 is attached to theseparator S1 for connecting the oxygen-containing gas flow field S2 andthe oxygen-containing gas passages S3 and S4, and preventing leakage ofthe reactant gas to the other fluid passages.

Stainless steel plates (SUS plate) S7 are provided to cover theconnection channels S6 a, S6 b for connecting the oxygen-containing gaspassages S3, S4, and the oxygen-containing gas flow field S2. Thestainless plates S7 have a rectangular shape, and having ears S7 a, S7 bat two positions, respectively. The ears S7 a, S7 b are fitted to thesteps S8 formed on the separator S1.

According to the disclosure of Japanese laid-open patent publication No.2001-266911, the stainless steel plates S7 cover the connection channelsS6 a, S6 b. Therefore, the polymer membrane (not shown) and the packingS5 are not deformed into the oxygen-containing gas flow field S2. Thedesired sealing performance is maintained, and the significant pressureloss of the reactant gas is prevented.

However, in the structure of Japanese laid-open patent publication No.2001-266911, the stainless steel plate S7 is attached to each of theconnection channels S6 a, S6 b of the separator S1. The operation ofattaching the stainless steel plate S7 to each of the connectionchannels S6 a, S6 b is laborious. When several tens to several hundredsof the power generation cells are stacked to form the fuel cell, theattaching operation of the stainless steel plate S7 is very laborious,time consuming, and thus, the production cost is large.

The stainless steel plates S7 are attached to the connection channels S6a, S6 b. Therefore, the width of the connection channels S6 a, S6 bneeds to be larger than the width of the stainless steel plates S7. Thesurface area of the electrode is not used efficiently. It is notsuitable to produce a compact and light fuel cell.

SUMMARY OF THE INVENTION

A general object of the present invention is to provide a fuel cell inwhich seal members on both surfaces of a separator are deformedsubstantially equally to the same extent, and the desired sealingperformance and the desired power generation performance are achieved.

A main object of the present invention is to provide a fuel cell with aneconomical and compact structure in which assembling operation of thefuel cell is performed simply, and the desired sealing performance andthe desired power generation performance are achieved.

According to the present invention, a fuel cell is formed by stackingpower generation cells each including an electrolyte electrode assemblyand separators sandwiching the electrolyte electrode assembly. Theelectrolyte electrode assembly includes first and second electrodes andan electrolyte interposed between the first and second electrodes. Areactant gas flow field is formed along an electrode surface forsupplying a reactant gas through the reactant gas flow field. A coolantflow field is formed between the power generation cells for supplying acoolant through the coolant flow field. A reactant gas passage extendsthrough the power generation cells, and is connected to the reactant gasflow field. A coolant passage extends through the power generationcells, and is connected to the coolant flow field.

A first seal is provided on one surface of the separator for sealing thereactant gas flow field. A second seal is provided on the other surfaceof the separator for sealing the coolant flow field.

The second seal includes a flow guide connecting the coolant flow fieldand the coolant passage, and the flow guide overlaps a section(overlapping section) of the first seal such that the separator issandwiched between the flow guide and the overlapping section of thefirst seal. When a load is applied to the flow guide and the overlappingsection in the stacking direction, the flow guide and the overlappingsection are substantially equally deformed in the stacking direction tothe same extent.

The first seal includes a flow guide connecting the reactant gas flowfield and the reactant gas passage, and the flow guide overlaps asection (overlapping section) of the second seal such that the separatoris sandwiched between the flow guide and the overlapping section of thesecond seal. When a load is applied to the flow guide and theoverlapping section in the stacking direction, the flow guide and theoverlapping section are substantially equally deformed in the stackingdirection to the same extent.

Thus, the first seal and the second seal on both surfaces of theseparator are substantially equally deformed to the same extent. Theload is uniformly applied in the surface of the power generation cell.The load balance does not change depending on the power generation cell.Thus, the stabilized power generation performance can be achieved. Theflow rates of the reactant gases and the coolant are uniform. Thestabilized power generation performance is achieved in each of the powergeneration cells.

The electrolyte electrode assembly includes the first and secondelectrodes and the electrolyte membrane interposed between the first andsecond electrodes. The surface area of the first electrode is smallerthan the surface area of the second electrode.

The first seal includes an inner seal provided between the electrolytemembrane and the separator, and an outer seal provided between adjacentseparators. The second seal includes an inner seal corresponding to theinner seal of the first seal, and an outer seal corresponding to theouter seal of the first seal. With this structure, the strength of thepower generation cell can be improved, and the thin power generationcell can be produced.

The line pressure of the flow guides and the line pressure of theoverlapping section are substantially the same, i.e., the pressure loadapplied to the flow guides per unit length, and the pressure loadapplied to the overlapping section per unit length are substantially thesame. The seal length of the flow guides and the seal length of theoverlapping section are substantially the same. With the simplestructure, the space in the power generation cell is provided uniformly,and the space between the power generation cells is provided uniformly.The reactant gas and the coolant flow through the connection channelssmoothly, and the desired sealing performance in the power generationcell is achieved.

The flow guides are oriented perpendicular to the overlapping section.The length of the flow guides is larger than the seal width of theoverlapping section. With the simple structure, when a load is appliedto the first and second seals, the first and second seals are deformedsubstantially equally to the same extent.

According to the present invention, a first seal member is providedintegrally on both surfaces of, and around an outer region of one of theseparators, and the second seal member is provided integrally on bothsurfaces of, and around an outer region of the other of the separators.The first seal member and the second seal member are in contact witheach other, and a channel connecting the reactant gas flow field and thereactant gas passage is formed between the first seal member and thesecond seal member.

The first seal member and the second seal member are in contact witheach other to form the channel between the reactant gas flow field andthe reactant gas passage. For example, the channel may be definedbetween a planar seal and a ridge-shaped seal, between ridge-shapedseals, between a planar seal and a circular or rectangular boss, orbetween bosses.

The first seal member and the second seal member function as the channelfor connecting the reactant gas flow field and the reactant gaspassages. Thus, dedicated metal plates such as the conventionalstainless steel plate (SUS plate) are not required. It is not requiredto perform attaching operation of the metal plate. Thus, the fuel cellis assembled simply, and produced at a low cost, while the desiredsealing performance is achieved. The size of the channel is small.Therefore, the surface area of the power generation cell is usedefficiently, and the power generation in the fuel cell is performedefficiently.

The channel is defined by a plurality of flow guides provided integrallywith at least one of the first and second seal members, at a positionbetween the reactant flow field and the reactant gas passage. With thesimple and economical structure, the power generation cell achieves thedesired sealing performance and the desired power generationperformance. The flow guides function as back support members formaintaining the pressure applied to the other seal at the required levelfor sealing.

The first seal member and the second seal member are in contact witheach other, and a channel connecting the coolant flow guide and thecoolant passage is formed between the first seal member and second sealmember. The first seal member and the second seal member function as thechannel for connecting the coolant flow field and the coolant passages.Thus, dedicated metal plates such as the conventional stainless steelplate (SUS plate) are not required.

The channel is defined by a plurality of flow guides provided integrallywith at least one of the first and second seal members, at a positionbetween the coolant flow field and the coolant gas passage. With thesimple and economical structure, the power generation cell achieves thedesired sealing performance and the desired power generationperformance. The flow guides function as back support members.

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings in which preferredembodiments of the present invention are shown by way of illustrativeexample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing main components of apower generation cell of a fuel cell according to an embodiment of thepresent invention;

FIG. 2 is a cross sectional view showing main components in a part ofthe fuel cell;

FIG. 3 is a cross sectional view showing main components in another partof the fuel cell;

FIG. 4 is a front view showing a first metal separator of the powergeneration cell;

FIG. 5 is a front view showing one surface of a second metal separatorof the power generation cell;

FIG. 6 is a front view showing the other surface of the second metalseparator of the power generation cell;

FIG. 7 is a view showing an inlet channel of the power generation cellfor supplying an oxygen-containing gas;

FIG. 8 is a view showing an inlet channel of the power generation cellfor supplying a coolant;

FIG. 9 is a view showing relationship between a seal length L1 and aseal length L2;

FIG. 10 is a view showing the height difference after compression incontrast to the ratio between the seal length L1 and the seal length L2;

FIG. 11 is a view showing a sealing structure disclosed in Japaneselaid-open patent publication No. 8-148169;

FIG. 12 is a view showing a part of a conventional separator; and

FIG. 13 is a view showing a sealing structure disclosed in Japaneselaid-open patent publication No. 2001-266911.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is an exploded perspective view showing main components of apower generation cell 12 of a fuel cell 10 according to an embodiment ofthe present invention. FIG. 2 is a cross sectional view showing a fuelcell 10 formed by stacking a plurality of the power generation cells 12in a direction indicated by an arrow A.

As shown in FIGS. 2 and 3, the fuel cell 10 is formed by stacking thepower generation cells 12 in the direction indicated by the arrow A. Atopposite ends of the fuel cell 10 in the stacking direction, end plates14 a, 14 b are provided. The end plates 14 a, 14 b are fixed to the fuelcell 10 by tie rods (not shown) for tightening the power generationcells 12 with a predetermined tightening force in the directionindicated by the arrow A.

As shown in FIG. 1, the power generation cell 12 includes a membraneelectrode assembly (electrolyte electrode assembly) 16 and first andsecond metal separators 18, 20 sandwiching the membrane electrodeassembly 16. For example, the first and second metal separators 18, 20are steel plates, stainless steel plates, aluminum plates, plated steelsheets, or metal plates having anti-corrosive surfaces by surfacetreatment. The first and second metal separators 18, 20 have a thicknessranging from, e.g., 0.05 mm to 1.0 mm.

As shown in FIG. 1, at one horizontal end of the power generation cell12 in a direction indicated by an arrow B, an oxygen-containing gassupply passage 30 a for supplying an oxygen-containing gas, a coolantdischarge passage 32 b for discharging a coolant, and a fuel gasdischarge passage 34 b for discharging a fuel gas such as ahydrogen-containing gas are arranged vertically in a direction indicatedby an arrow C. The oxygen-containing gas supply passage 30 a, thecoolant discharge passage 32 b, and the fuel gas discharge passage 34 bextend through the power generation cell 12 in the stacking directionindicated by the arrow A.

At the other horizontal end of the power generation cell 12 in thedirection indicated by the arrow B, a fuel gas supply passage 34 a forsupplying the fuel gas, a coolant supply passage 32 a for supplying thecoolant, and an oxygen-containing gas discharge passage 30 b fordischarging the oxygen-containing gas are arranged vertically in thedirection indicated by the arrow C. The fuel gas supply passage 34 a,the coolant supply passage 32 a, and the oxygen-containing gas dischargepassage 30 b extend through the power generation cell 12 in thedirection indicated by the arrow A.

The membrane electrode assembly 16 comprises an anode 38, a cathode 40,and a solid polymer electrolyte membrane 36 interposed between the anode38 and the cathode 40. The solid polymer electrolyte membrane 36 isformed by impregnating a thin membrane of perfluorosulfonic acid withwater, for example. The surface area of the anode 38 is smaller than thesurface area of the cathode 40.

Each of the anode 38 and cathode 40 has a gas diffusion layer such as acarbon paper, and an electrode catalyst layer of platinum alloysupported on porous carbon particles. The carbon particles are depositeduniformly on the surface of the gas diffusion layer. The electrodecatalyst layer of the anode 38 and the electrode catalyst layer of thecathode 40 are fixed to both surfaces of the solid polymer electrolytemembrane 36, respectively.

The first metal separator 18 has an oxygen-containing gas flow field(reactant gas flow field) 42 on its surface 18 a facing the membraneelectrode assembly 16. The oxygen-containing gas flow field 42 includesa plurality of grooves extending in a serpentine pattern such that theoxygen-containing gas flows in the direction indicated by the arrow B,and turns upwardly, for example (see FIGS. 1 and 4). Theoxygen-containing gas flow field 42 is connected to theoxygen-containing gas supply passage 30 a at one end, and connected tothe oxygen-containing gas discharge passage 30 b at the other end. Asshown in FIG. 5, the second metal separator 20 has a fuel gas flow field(reactant gas flow field) 44 on its surface 20 a facing the membraneelectrode assembly 16. The fuel gas flow field 44 includes a pluralityof grooves extending in a serpentine pattern such that the fuel gasflows in the direction indicated by the arrow B, and turns upwardly. Thefuel gas flow field 44 is connected to the fuel gas supply passage 34 aat one end, and connected to the fuel gas discharge passage 34 b at theother end.

As shown in FIGS. 1 and 6, a coolant flow field 46 is formed between asurface 18 b of the first metal separator 18 and a surface 20 b of thesecond metal separator 20. The coolant flow field 46 includes aplurality of grooves extending straight in the direction indicated bythe arrow B. The coolant flow field 46 is connected to the coolantsupply passage 32 a at one end, and connected to the coolant dischargepassage 32 b at the other end.

As shown in FIGS. 1 and 4, a first seal member 50 is formed integrallyon the surfaces 18 a, 18 b of the first metal separator 18 to cover(sandwich) the outer edge of the first metal separator 18. The firstseal member 50 is made of seal material, cushion material or packingmaterial such as EPDM (Ethylene Propylene Diene Monomer), NBR (NitrileButadiene Rubber), fluoro rubber, silicon rubber, fluoro silicon rubber,butyl rubber (Isobutene-Isoprene Rubber), natural rubber, styrenerubber, chloroprene rubber, or acrylic rubber.

The first seal member 50 includes a first planar section 52 on thesurface 18 a of the first metal separator 18, and a second planarsection 54 on the surface 18 b of the first metal separator 18. Thesecond planar section 54 is larger than the first planar section 52.

As shown in FIG. 2, the first planar section 52 is provided around themembrane electrode assembly 16 such that the first planar section 52 isspaced from an outer edge of the membrane electrode assembly 16. Thesecond planar section 54 is provided around the membrane electrodeassembly 16 such that the second planar section 54 partially overlapsthe anode 40. As shown in FIG. 4, the first planar section 52 is notprovided between the oxygen-containing gas supply passage 30 a and theoxygen-containing gas flow field 42, and between the oxygen-containinggas discharge passage 30 b and the oxygen-containing gas flow field 42.Thus, the oxygen-containing gas supply passage 30 a and theoxygen-containing gas discharge passage 30 b are connected to theoxygen-containing gas flow field 42. Further, the second planar section54 is provided such that the coolant supply passage 32 a is connected tothe coolant discharge passage 32 b.

As shown in FIG. 5, a second seal member 56 is formed integrally on thesurfaces 20 a, 20 b of the second metal separator 20 to cover (sandwich)the outer edge of the second metal separator 20. Specifically, thesecond seal member 56 includes an outer seal (first seal) 58 a providedon the surface 20 a, and near the outer edge of the second metalseparator 20, and an inner seal (first seal) 58 b provided at apredetermined distance inwardly from the outer seal 58 a.

The outer seal 58 a and the inner seal 58 b may have various shapes,including tapered shape (lip shape), trapezoid shape, or half-cylindershape. The outer seal 58 a is in contact with the first planar section52 formed on the first metal separator 18, and the inner seal 58 b isdirectly in contact with the solid polymer electrolyte membrane 36 ofthe membrane electrode assembly 16.

As shown in FIG. 5, the outer seal 58 a is formed around theoxygen-containing gas supply passage 30 a, the coolant discharge passage32 b, the fuel gas discharge passage 34 b, the fuel gas supply passage34 a, the coolant supply passage 32 a, and the oxygen-containing gasdischarge passage 30 b. The inner seal 58 b is formed around the fuelgas flow field 44. The outer edge of the membrane electrode assembly 16is positioned between the inner seal 58 b and the outer seal 58 a.

An outer seal (second seal) 58 c corresponding to the outer seal 58 aand an inner seal (second seal) 58 d corresponding to the inner seal 58b are provided on the surface 20 b of the second separator 20 (see FIG.6). The shapes of the outer seal 58 c and the inner seal 58 d aresimilar to the shapes of the outer seal 58 a and the inner seal 58 b.

As shown in FIG. 5, the outer seal 58 a has an inlet channel 60connecting the oxygen-containing gas supply passage 30 a and theoxygen-containing gas flow field 42. Further, the outer seal 58 a has anoutlet channel 62 connecting the oxygen-containing gas discharge passage30 b and the oxygen-containing gas flow field 42.

The inlet channel 60 is formed by a plurality of flow guides 64 arrangedseparately in the direction indicated by the arrow C. The flow guides 64are oriented in the direction indicated by the arrow B. The flow guides64 are in contact with the first planar section 52 to form passages forthe oxygen-containing gas between the flow guides 64 (see FIG. 3).Likewise, the outlet channel 62 of the outer seal 58 is formed by aplurality of flow guides 66 oriented in the direction indicated by thearrow B. The flow guides 66 are in contact with the first planar section52 to form passages for the oxygen-containing gas between the flowguides 66.

As shown in FIG. 7, the flow guides 64 at the inlet channel 60 formed onthe surface 20 a of the second metal separator 20 overlap a section 68of the outer seal 58 c formed on the surface 20 b of the second metalseparator 20. Stated otherwise, the overlapping section 68 is part ofthe outer seal 58 c which overlaps the flow guides 64 of the outer seal58 a such that the second metal separator 20 is sandwiched between theoverlapping section 68 and the flow guides 64. The flow guides 64 areoriented perpendicularly to the overlapping section 68. Thus, the lengthof the flow guides 64 is larger than the seal width of the outer seal 58c. When a load is applied to the flow guides 64 and the overlappingsection 68, the flow guides 64 and the seal overlapping sections 68 aredeformed substantially equally in the stacking direction to the sameextent.

Specifically, the line pressure of the flow guides 64 and the linepressure of the overlapping section 68 are substantially the same, i.e.,the pressure load applied to the flow guides 64 per unit length, and thepressure load applied to the overlapping section 68 per unit length aresubstantially the same. The seal length L1 of the flow guides 64 and theseal length L2 of the overlapping section 68 are substantially the same.The seal length L2 is a partial length of the seal overlapping section68, corresponding to the interval between the flow guides 64. As long asthe flow guides 64 and the overlapping section 68 have substantially thesame spring constant, the material of the flow guides 64 and material ofthe overlapping section 68 may be different. Therefore, variousmaterials can be used for the flow guides 64 and the overlapping section68.

The outlet channel 62 and the inlet channel 60 have substantially thesame structure. The flow guides 64 on the surface 20 a of the secondmetal separator 20 overlap a seal section 70 of the outer seal 58 cformed on the surface 20 b of the second metal separator 20. When a loadis applied to the flow guides 64 and the seal overlapping section 70 inthe stacking direction, the flow guides 64 and the overlapping section70 are substantially equally deformed in the stacking direction to thesame extent (see FIG. 5).

As shown in FIG. 6, an inlet channel 72 connecting the coolant supplypassage 32 a and the coolant flow field 46, and an outlet channel 74connecting the coolant discharge passage 32 b and the coolant flow field46 are formed on the surface 20 b of the second metal separator 20. Theinlet channel 72 is formed by a plurality of flow guides 76 arrangedseparately in the direction indicated by the arrow B as part of theouter seal 58 c and the inner seal 58 d. The flow guides 78 are orientedin the direction indicated by the arrow C. Likewise, the outlet channel74 is formed by a plurality of flow guides 78 arranged separately in thedirection indicated by the arrow C as part of the outer seal 58 c andthe inner seal 58 d. The flow guides 76, 78 are in contact with thesecond planar section 54, and passages for the coolant is formed betweenthe flow guides 76, 78, respectively.

As shown in FIG. 8, the flow guides 76 of the inlet channel 72 on thesurface 20 b of the second metal separator 20 overlap a section 80 a ofthe outer seal 58 a and a section 80 b of the inner seal 58 b on thesurface 20 a such that the second metal separator 20 is sandwichedbetween the flow guides 76 and the overlapping sections 80 a, 80 b. Whena load is applied to the flow guides 76 of the inlet channel 72 and theoverlapping sections 80 a, 80 b in the stacking direction, the flowguides 76 and the overlapping sections 80 a, 80 b are substantiallyequally deformed to the same extent. The seal length L3 is equal to thesum of the seal length L4 of the overlapping section 80 a and the seallength L5 of the overlapping section 80 b (L3=L4+L5). The seal length L4is a partial length of the seal overlapping section 80 a, correspondingto the interval between the flow guides 76, and the seal length L5 is apartial length of the overlapping section 80 b, corresponding to theinterval between the flow guides 76. In FIG. 8, each of the flow guides76 overlaps both of the overlapping sections 80 a, 80 b. Alternatively,the flow guides 76 may be provided separately such that one flow guide76 overlap only one of the overlapping sections 80 a, 80 b.

Likewise, as shown in FIG. 6, the flow guides 78 on the surface 20 a ofthe second metal separator 20 overlap a section 82 a of the outer seal58 a and a section 82 b of the inner seal 58 b such that the secondmetal separator 20 is sandwiched between the flow guides 78 and theoverlapping sections 82 a, 82 b. When a load is applied to the flowguides 78 and the overlapping sections 82 a, 82 b in the stackingdirection, the flow guides 78 and the overlapping sections 82 a, 82 bare deformed substantially equally at a same extent.

As shown in FIG. 6, an inlet channel 84 is provided near the fuel gassupply passage 34 a, and an outlet channel 86 is provided near the fuelgas discharge passage 34 b. The inlet channel 84 is formed by aplurality of flow guides 88 arranged in the direction indicated by thearrow C. The outlet channel 86 is formed by a plurality of flow guides90 arranged in the direction indicated by the arrow C. The flow guides88, 90 are in contact with the second planar section 54, and formpassages for the fuel gas between the flow guides 88 and 90,respectively.

The flow guides 88 overlap a section 92 a of the outer seal 58 a and asection 92 b of the inner seal 58 b such that the second metal separator20 is sandwiched between the flow guides 88 and the overlapping sections92 a, 92 b. Likewise, the flow guides 90 overlap a section 94 a of theouter seal 58 a and a section 94 b of the inner seal 58 b such that thesecond metal separator 20 is sandwiched between the flow guides 90 andthe overlapping sections 94 a, 94 b.

The inlet channel 84 and the outlet channel 86 have the same structureas the inlet channel 72. When a load is applied to the flow guides 88and the overlapping sections 92 a, 92 b, and the flow guides 90 and theoverlapping sections 94 a, 94 b in the stacking direction, the flowguides 88 and the overlapping sections 92 a, 92 b, and the flow guides90 and the overlapping sections 94 a, 94 b are deformed substantiallyequally to the same extent. A plurality of supply holes 96 and dischargeholes 98 are provided outside the inner seal 58 d, near the inletchannel 84 and the outlet channel 86, respectively. The supply holes 96extend through the second separator 20, and are connected to the inletof the fuel gas flow field 44. The discharge holes 98 extend through thesecond separator 20, and are connected to the outlet of the fuel gasflow field 44. The inlet and outlet of the fuel gas flow field 44 arepositioned inside the inner seal 58 b on the surface 20 a of the secondmetal separator 20 (see FIG. 5).

Operation of the fuel cell 10 will be described below.

As shown in FIG. 1, an oxygen-containing gas is supplied to theoxygen-containing gas supply passage 30 a, and a fuel gas such as ahydrogen-containing gas is supplied to the fuel gas supply passage 34 a.Further, a coolant such as pure water, an ethylene glycol or an oil issupplied to the coolant supply passage 32 a.

The oxygen-containing gas flows from the oxygen-containing gas supplypassage 30 a into the oxygen-containing gas flow field 42 of the firstmetal separator 18 (see FIG. 3). Then, the oxygen-containing gas flowsin a serpentine pattern in the direction indicated by the arrow B, andmoves upwardly along the cathode 40 of the membrane electrode assembly16 for inducing an electrochemical reaction at the cathode 40. The fuelgas flows from the fuel gas supply passage 34 a into the fuel gas flowfield 44 of the second metal separator through the supply holes 96 (seeFIG. 2). The fuel gas flows in a serpentine pattern in the directionindicated by the arrow B, and moves upwardly along the anode 38 of themembrane electrode assembly 16 for inducing an electrochemical reactionat the anode 38.

Thus, in the membrane electrode assembly 16, the oxygen-containing gassupplied to the cathode 40, and the fuel gas supplied to the anode 38are consumed in the electrochemical reactions at catalyst layers of thecathode 40 and the anode 38 for generating electricity.

After the oxygen in the oxygen-containing gas is consumed at the cathode40, the oxygen-containing gas is discharged into the oxygen-containinggas discharge passage 30 b in the direction indicated by the arrow A.Likewise, after the fuel gas is consumed at the anode 38, the fuel gasis discharged through the discharge holes 98 into the fuel gas dischargepassage 34 b in the direction indicated by the arrow A.

The coolant from the coolant supply passage 32 a flows into the coolantflow field 46 between the first and second metal separators 18, 20, andflows in the direction indicated by the arrow B for cooling the membraneelectrode assembly 16. Then, the coolant is discharged into the coolantdischarge passage 32 b.

In the present embodiment, the inlet channel 60 including the flowguides 64 are provided on the surface 20 a of the second metal separator20 for smoothly supplying the oxygen-containing gas from theoxygen-containing gas supply passage 30 a to the oxygen-containing gasflow field 42. As shown in FIG. 5, the flow guides 64 of the inletchannel 60 are part of the outer seal 58 b, and the section 68 on thesurface 20 b of the second separator 20 overlaps the flow guides 64 ofthe inlet channel 60. The overlapping section 68 is part of the outerseal 58 c. The overlapping section 68 and the flow guides 64 areresilient, and deform easily.

As shown in FIG. 7, the line pressure of the flow guides 64 of the inletchannel 60 and the line pressure of the overlapping section 68 aresubstantially the same. The seal length L1 of the flow guides 64 and theseal length L2 of the overlapping section 68 are substantially the same.Therefore, when a load is applied to the flow guides 64 and theoverlapping section 68 provided opposite surfaces 20 a, 20 b of themetal separator 20 in a stacking direction of the power generation cells12, the flow guides 64 and the overlapping section 68 are deformedequally in the stacking direction to the same extent.

Specifically, when the seal length L1 of the flow guides 64 and the seallength L2 of the overlapping section 68 are changed as shown in FIG. 9,the height difference in contrast to the ratio between the seal lengthand the seal length changes as shown in FIG. 10. The height differenceis the difference between the height of the flow guides 64 and theheight of the overlapping section 68 after compression by applying theload to the flow guides 64 and the overlapping section 68 in thestacking direction. If the ratio of the seal length L1 and the seallength L2 (L1/L2) is about 1.0, i.e., the seal length L1 is equal to theseal length L2, the height difference is zero.

The flow guides 64 and the overlapping section 68 on both surfaces 20 a,20 b of the second metal separator 20 are deformed substantially equallyto the same extent. The line pressure (load) applied to the second metalseparator 20 is well-balanced, and thus, the second metal separator 20is not deformed undesirably. The flow guides 64 of the inlet channel 60are deformed uniformly. Thus, the oxygen-containing gas is supplied fromthe oxygen-containing gas supply passage 30 a to the oxygen-containinggas flow field 42 smoothly.

The outlet channel 62 has substantially the same structure as the inletchannel 60. When a load is applied to the flow guides 66 and theoverlapping section 70 provided opposite surfaces 20 a, 20 b of themetal separator 20 in the stacking direction, the flow guides 66 and theoverlapping section 70 are deformed substantially equally in thestacking direction to the same extent. Thus, the second metal separator20 is not deformed undesirably, and the exhaust gas (the consumedoxygen-containing gas) is reliably discharged from the oxygen-containinggas flow field 42 to the oxygen-containing gas discharge passage 30 b.

As shown in FIG. 6, the second metal separator 20 has the inlet channel72 on the surface 20 b for connecting the coolant supply passage 32 aand the coolant flow field 46. The flow guides 76 of the inlet channel72 and the sections 80 a, 80 b on the opposite surface 20 b of thesecond metal separator 20 are overlapped with each other. When a load isapplied to the flow guides 76 of the inlet channel 72 and theoverlapping sections 80 a, 80 b, the flow guides 76 and the overlappingsections 80 a, 80 b are deformed substantially equally in the stackingdirection to the same extent. As shown in FIG. 8, the seal length L3 ofthe flow guides 76 is equal to the sum of the seal length L4 of the ofthe overlapping section 80 a and the seal length L5 of the overlappingsection 80 b (L3=L4+L5).

Since the flow guides 76 of the inlet channel 72 and the overlappingsections 80 a, 80 b are deformed substantially equally to the sameextent, the second metal separator 20 between flow guides 76 of theinlet channel 72 and the overlapping sections 80 a, 80 b is notdeformed. Consequently, the coolant is supplied smoothly from thecoolant supply passage 32 a to the coolant flow field 46.

The outlet channel 74 has substantially the same structure as the inletchannel 72. The flow guides 78 and sections 82 a, 82 b are deformedsubstantially equally to the same extent. Therefore, the coolant isdischarged into the coolant discharge passage 32 b smoothly.

As shown in FIG. 6, the inlet channel 84 connects the fuel gas supplypassage 34 a and the fuel gas flow field 44, and the outlet channel 86connects the fuel gas discharge passage 34 b and the fuel gas flow field44. The flow guides 88, 90, and the overlapping sections 92 a, 92 b, 94a, 94 d are deformed substantially equally to the same extent.Therefore, the fuel gas is smoothly supplied from the fuel gas supplypassage 34 a to the fuel gas flow field 44, and smoothly discharged fromthe fuel gas flow field 44 to the fuel gas discharge passage 34 b. Thesecond metal separator 20 is not deformed undesirably.

According to the present embodiment, the power generation in the fuelcell 10 is performed stably. With the simple structure, the flow ratesof the fuel gas, the oxygen-containing gas, and the coolant are stablymaintained at the desired levels, respectively. Consequently, the powergeneration is stably performed in each of the power generation cells 12.

According to the present embodiment, as shown in FIG. 3, the flow guides64 are in contact with the first planar section 52 formed on the surface18 a of the first metal separator 18 to form passages for theoxygen-containing gas between the flow guides 64.

The inlet channel 60 is covered by part (flow guides 64) of the secondseal member 56 and part (first planar section 52) of the first sealmember 50. Thus, dedicated metal plates such as the conventionalstainless steel plate (SUS plate) are not required for covering theinlet channel 60, and it not required to attach such metal plate. Thus,the fuel cell 10 is assembled simply, and produced at a low cost, whilethe desired sealing performance is achieved.

The size of the inlet channel 60 is small. Therefore, the surface areaof the power generation cell 12 is used efficiently, and the powergeneration in the fuel cell 10 is performed efficiently.

The flow guides 64 of the inlet channel 60 are formed on the second sealmember 56. With the simple and economical structure, the powergeneration cell 12 achieves the desired sealing performance and thedesired power generation performance. The flow guides 64 functions asback support members for maintaining the pressure applied to the section60 of the outer seal 58 c at the required level for sealing.

The outlet channel 62 has the similar functions as the inlet channel 60.Further, the inlet channels 72, 84, and the outlet channels 74, 86 havethe similar functions.

The first seal member 50 and the second seal member 56 are in contactwith each other to form the inlet channel 60. Alternatively, the channelmay be defined between a planar seal and a ridge-shaped seal, betweenridge-shaped seals, between a planar seal and a circular or rectangularboss, or between bosses.

While the invention has been particularly shown and described withreference to preferred embodiments, it will be understood thatvariations and modifications can be effected thereto by those skilled inthe art without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A fuel cell formed by stacking a plurality of power generation cellsin a stacking direction, wherein each of said plurality of powergeneration cells includes an electrolyte electrode assembly and metalseparators sandwiching said electrolyte electrode assembly, saidelectrolyte electrode assembly including an anode and a cathode and anelectrolyte interposed between said anode and said cathode, wherein areactant gas flow field is formed along an electrode surface forsupplying a reactant gas through said reactant gas flow field; a coolantflow field is formed between said power generation cells for supplying acoolant through said coolant flow field; a reactant gas passage extendsthrough said power generation cells, and is connected to said reactantgas flow field; a coolant passage extends through said power generationcells, and is connected to said coolant flow field; a first seal isprovided on a top surface of one of said metal separators for sealingsaid reactant gas flow field; a second seal is provided on a bottomsurface of said metal separator for sealing said coolant flow field,wherein said bottom surface is spaced apart from and parallel to saidtop surface, said bottom surface and said top surface of said metalseparator extend perpendicular to the stacking direction; said firstseal includes a flow guide made of a same material as said first seal,said flow guide connecting said reactant gas flow field and saidreactant gas passage, and said flow guide provided on said top surfaceoverlaps a continuous section of said second seal provided on saidbottom surface such that said separator is sandwiched between said flowguide and said continuous overlapping section of said second seal,wherein the flow guide and the continuous overlapping section areresilient; wherein a line pressure of said flow guide and a linepressure of said continuous overlapping section are substantially thesame, and wherein a seal length of said flow guide and a seal length ofsaid continuous overlapping section are substantially the same such thatwhen a load is applied to said flow guide and said continuousoverlapping section in the stacking direction, said flow guide and saidcontinuous overlapping section are substantially equally deformed in thestacking direction to the same extent.
 2. A fuel cell according to claim1, wherein said electrolyte is an electrolyte membrane, and a surfacearea of said anode is smaller than a surface area of said cathode; andsaid first seal includes an inner seal provided between said electrolytemembrane and said separator, and an outer seal provided between adjacentseparators.
 3. A fuel cell according to claim 2, wherein said secondseal includes an inner seal corresponding to said inner seal of saidfirst seal; and an outer seal corresponding to said outer seal of saidfirst seal.
 4. A fuel cell according to claim 1, wherein said flow guideis oriented perpendicularly to said continuous overlapping section, andlength of said flow guide is larger than width of said continuousoverlapping section.